1. Field of the Invention
Dental handpieces having gas-driven motors are well known. Of particular interest herein is a high-speed gas-driven dental handpiece having decreased noise and improved vibration damping characteristics.
2. State of the Art
During use of a high-speed gas-driven dental handpiece, rotor speeds are attained of 250,000 to 400,000 r.p.m. or more. While these high speed motors provide increased working efficiency as compared to lower speed motors for many dental applications, the substantially increased amounts of noise or vibration, or both, generated by the high speed motor can be quite disturbing to dentist and patient alike. Also, at certain critical rotor operating speeds, resonance effects between the motor and other portions of the dental handpiece may substantially intensify or amplify the noise or vibration originating from the gas driven motor.
It is a requirement of a dental handpiece that the handle portion provide a user with good tactile control over the instrument to ensure safe and efficient dental work within a patient's mouth. One aspect of good tactile control is provided by a handle portion having sufficient rigidity to ensure positive and direct transmittal of forces from the user's hand to the work site within the patient's mouth. It is a problem, however, that with currently available dental handpieces having rigid handle portions, vibration is readily transmitted from the motor housing of the handpiece to the hand-grippable portion of the handle.
Several attempts have been made to reduce the noise or vibration that may originate from a high-speed gas-driven motor. For example, in U.S. Pat. No. 3,499,223 to Lieb et al there is disclosed a high speed dental handpiece having vibration damping rings fabricated of non-metallic, rubbery materials interposed between the metallic rotor bearings and a metallic motor housing. These vibration damping rings tend to inhibit transfer of vibration from the rotating elements of a high speed motor to its housing. Further improvements in the arrangement of vibration damping elements upon a turbine cartridge assembly of a high-speed gas-driven motor are disclosed in U.S. application Ser. No. 947,215 of F. W. Kerfoot, Jr., filed on Sept. 29, 1978, the disclosure of which is incorporated herein by reference.
Though the interposition of vibration damping elements between a turbine rotor assembly and a motor housing tends to inhibit transfer of vibration or noise, total isolation of the rotating elements from the non-rotating elements of a handpiece is difficult to attain inasmuch as some rigid connection between the rotor and the housing is necessary for proper rotor alignment or for static preloading of rotor bearings within the housing. Hence, there remains a problem of transfer of vibration from the rotor to the motor housing and the consequent problem of resonance-effects enhancement at certain critical speeds between the gas-driven motor and other portions of the dental handpiece, such as the hand-grippable portion.
There is need, therefore, for a high-speed dental handpiece in which a gas-driven motor is substantially completely isolated from a handle portion with respect to transfer of vibration, so that the transfer of vibration from the gas-driven motor to the handle portion and the consequent generation of noise may be minimized during use of the dental handpiece, without significant decreases in user tactile control over the handpiece.